Yes you can make as many new ground segments as you want by doing what you say.
Heres a little kinda tutorial if it helps. I do hope so.
Find the default ground segment folder and copy the segment and its associated script file and editor icon bmp (3 items) to a new folder - call it My Segments or whatever you want. Rename all of the files. Call your new files ground2 or something. Open the ground script and look for where the texture path is located and point your script to the same location where you would place your new texture. If theres not one indicated the simply keep your new texture in the same place as your other new ground2 files i.e. My Segments. Then in the script file indicate the location like this texturepath = mytexture.dds which does not indicate a path as such but shows FPSC that its in the same directory as everything else related to the ground segment. (except the .x files)
In FPSC it does not seem to matter where things are kept as long as the locations are indicated correctly in script (no mispellings) and FPSC can find the things it needs. If no path is indicated then FPSC will look for the files in the directory the script is located in first. If the textures or other files cannot be located then you will have something not working of course.
This procedure is relatively simple and will work for any segment not just ground segments.(similar procedure too for entities).
To replace textures on any default segment follow the same procedures by copying all associated files as said and renaming and changing if necessary all path indications to your new files.
Two important points :
1.If you are using default stuff as a basis for creating new - remember there will be no need to create new .x files (unless you want new ones with different shapes) as you can use the same x.file for creating multiple instances of an object - in essence you are just creating new ones by changing the skins or textures (viisual appearance,), script file and editor icon. That way you save a lot of game size and memeory as you are using multiple instances of only single x.file objects. Using the default x.files this way you dont have to create any new copies of segment .x files or change any path references to the default ones.
2. Dont overwrite default files alway make copies and always have backups of the default stuff.
Have fun
